Production of acrylic acid



"Patented jan 7,1947

, .L tary of Agriculture No Drawing;

(Granted This application made ,under the act "of March 3, 1883, asamended by the, act of,April 30, 1928, andthe. invention hereindescribed, if

' patented, may be manufactured and used by or for theGovernme'nt -oi'the United States oi America for governmental purposes without thepayment to us of any royalty thereon.

This invention relates to the production of unsaturated acids by theacidolysis of unsaturated esters, and particularly to the-production ofacrylic acid by the reaction of an ester of acrylic acid with anorganicacid other thanthe acid tobe formed, in particular, with asaturated aliphatic acid such as formic acid or acetic acid. Thepreparation of dry acrylic acid in high yields in accordance with thepresent known methods is diflicultt Hydrolysis of methyl acrylate orethyl acrylate yields various side products in addition to the desiredacrylic acid, and the acrylic acid ter. I

This invention has among its objects the preparation of dryacrylic'acid' under essentially anhydrous conditions in high yields byacidolysis of esters of acrylic acid with anhydrous organic acid otherthan the acrylic acids prepared; and such other objects as willlbeapparent from the following description and claims. 3

In accordance with the invention, dry acrylic acid is preferablyproduced by reacting by mix, ing and heating a suitable ester of acrylicacid with an anhydrous saturated aliphatic acid in the presence of amineral acid esteriflcation catalyst and a polymerization' inhibitor,and'removing the by-product ester, which is produced by replacement ofthe hydrogen of the carboxylic group of the saturated aliphatic acidemployed with the acrylic ester group, as the by-product "ester isformed. For example, when methyl acrylate and anhydrous formic acid arereacted,

the by-product, methylformate, is distilled until the reaction'iscomplete, andtheformed acrylic acid'isthen rectified.

The process is exhibited by the following example:

. r 7 Example Four moles (184 produced is contaminated with wa g.) offormic acid, 12 moles presented by the Score- Application November 11,1944,

SerialNo. 563,047 i scala (01, 260526) under the act cf-March 3,1883, asf amended April 30, 1928: 370 0. G. 757) product, methyl Iormate, wasthen slowly with drawn as formed until its production ceased (8 to 10hours). The excess methyl acrylate was then distilled at a pressure of140 mm., after which the formed acrylic acid was distilled at 56 C. (25mm.). The yield was 231 g. (80 per- 1 cent of the theoretical based onthe formic acid Over 91 percent 01' the methyl acrylateused). put intothe reaction mixture was either recovered or converted into acrylicacid.

When acetic acid and unsubstituted methyl acrylate were reacted in asimilar manner, acrylic the rate of acidacid was obtained, althougholysis was slower. Y

The process is not limited to the specific reagents and conditions givenabove. Other mineral acid catalysts maybe used instead of the sulfuricacid, and various polymerization inhibitors may be substituted for thehydroquinone. Entraining agents may be used to facilitate thedistillation oi the various fractions. Various other. acids, such asbutyric acid, benzoic acid, boric acid, and lactic acid may be usedinstead of the formic acid or the acetic acid, and other esters ofacrylic acid, particularly alkyl acrylates, may be used in place of the,methy1 acrylate. Also, other estersv of higher series may be used, suchas esters of crotonic acid, to produce crotonic acid, althoughpreferably, for purposes of fractional distillation, the reacting acidsand esters should be so selected that the produced byproduct ester boilsat the lowest boiling point,

' the excess reacting ester boils next, and the iormed unsaturated acidboils at the highest point.

' Either continuous or batch operation may be used, but'it is preferredthat the formed byproduct ester be removed continuously in the mannerindicated.

Having thus described the invention, what is claimed-is:

1. A process of preparing dry acrylic acid comprising mixing and heatingan ester of acrylic acid with a saturated aliphatic acid under anhydrousconditions in the presence of a mineral acid ,esteriilcation catalystand a. polymerization (1032 g.) of unsubstituted methyl acrylate (an"still was operated wlthtotal reflux until the tem-' perature at thestill-head fell to 32 C. The byinhibitor, and removing the by-productester which is produced as it is formed.

2. A process of preparing dry acrylic acid comprising mixing and heatingan alkyl acrylate with a saturated aliphatic acid under anhydrousconditions in the presence of a mineral acid esterification catalyst,and a polymerization inhib- 8. A process otjpreparing-dry acrylic acidc0m-- prising mixlng'and heatingmethylacrylate with a'saturatedaliphaticacid under'anhydrous oon-,

ditions in the presence; or amineral acid esteriflcation catalyst and apolymerisation inhib. itor. and removing the try-product ester which isproduced as it is tor-med;

4. A process 01' preparing presence of a mineral acid esteriflcationcatalyst and a polymerization-inhibitor. and removingthe by-product,methyl tormateras it is formed.

5. A process of preparing dry acrylic acidcomprising mixing and heatingan excess of an alkyl acrylate having a lower boilingpoint than acrylicacid with a saturated aliphatic acid under anhydrous conditions in thepresence of minerltl acid esteriiication catalyst and a polymerizationinhibitor, removing'the by-product ester dryacrylic acidicomprisingmixing and'heating-methylacrylate with formic acid under anhydrousconditions in the which is producedasit is formed, and then fractionallydistilling the reaction mass to separate theexcess alkyl acrylate fromthe formed acrylic CHESSIE E. REHBERG. CHARLES H. FISHER.

